Appearance of the hair has long been an important aspect of human grooming. It is, in fact, one of the first characteristics that humans notice about one another. The length, thickness, volume, color, and texture all play critical roles in the appearance of hair. Hair also affects self-esteem, which may account for the degree of attention that it receives. Persons having hair that is unmanageable, dry, oily, limp, or otherwise unconventional in appearance, regardless of the source of these problems, often seek products to address these problems. A multi-billion dollar industry has evolved to provide products that help enhance volume, shine, bounce, and manageability of hair. Such products include shampoos, conditioners, styling aids, hair sprays, hair colorants, perms, straighteners and the like.
In addition to this cosmetic market, there is a separate market for products to treat thinning hair and baldness. Although not all the products that are marketed in this segment are drug products, the predominant products are pharmaceuticals such as Rogaine® and Regaine® (topical solutions of the drug minoxidil from Upjohn, Inc.), Propecia® and Proscar® (orally ingested tablet of the drug finasteride from Merck and Company, Inc.), Andolactone® (orally ingested tablets or topical solutions of the drug sprionolactone from G. D. Searle, Inc.), Androcur® (orally ingested tablet of the drugs cyproterone acetate and ethinyl estradiol from Schering-Plough, Inc.), Eulexin® (oral tablets of the drug flutamide from Schering-Plough, Inc.). Additionally, oral contraceptives (containing estrogens and/or estradiol), tretinoin, and azelaic acid are drugs that have been the subject of scientific studies for their potential to enhance hair growth. There are also a variety of other products on the market today that claim to aid in the growth of hair.
Hair is a specialized cylindrical structure primarily composed of keratinized proteins, but it also contains a variety of other materials, such as minerals. Each hair is composed of two primary layers. The outmost layer, called the cuticle, is composed of a series of overlapping, visibly transparent platelets. These platelets are oriented in such a way that their exposed end is directed toward the distal end of the hair (the end furthest from the scalp). The cuticle completely surrounds the inner layer, which is known as the cortex. This inner layer is made of elongated strands of keratinized protein that is formed into bundles. Disulfide (—S—S—) bonds between molecules of the amino acid cysteine link both within strands and between adjacent strands. These disulfide bonds are responsible for the strength, resiliency, and curliness of hair. Some hairs have a third innermost layer, called the medulla. This layer is composed of cellular debris generated during the process of keratinization. There are no known structural attributes associated with the medulla.
Because the hair is made of protein, it can be damaged by mechanical, chemical, and thermal injury. The cuticle is often the primary focus of that damage because combing, brushing, and other forms of mechanical manipulation tend to chip off portions of the cuticle. Exposure to low relative humidities and high temperatures caused by blow dryers, curling irons, straightening irons, and hot curlers dry the cuticle such that edges of these platelets lift up. This lifting of the cuticle creates tangles between hair fibers that in turn can cause the cuticle to break, especially during mechanical manipulation. Moreover, high temperatures caused by blow dryers, curling irons, and straightening irons also can cause blisters on the cuticle platelets that leave holes or cracks in them. High pH chemicals applied to the hair cause swelling of the cuticle and concomitant opening of the spaces between cuticle platelets. If this high pH is not thoroughly neutralized following such treatments, spaces between the cuticle platelets remain open and thereby reduce the barrier properties afforded by the cuticle layer. The breakage and loss of portions of the cuticle platelets are always greatest at the most distal portions of the hair strands. Therefore, it is not unusual, especially with longer hair, to find significant loss of the cuticle layer. The loss of cuticle platelets can also result in split ends, in which the strands of the cortex fray because they are not constrained by the presence of the cuticle layer.
Hair grows from follicles in the skin that extend from the epidermis (the outmost layer of skin) to the dermis (the deepest layer of the skin). Hair growth is a complex biochemical process that is only partially understood, in part because it is extremely difficult to isolate single hair follicles and grow them in culture medium. However, it is well recognized that hair grows from active hair follicles at a rate of 0.2 to 0.5 millimeters (0.01 to 0.02 inches) per day. Hair growth is not a continuous phenomenon, but rather occurs in cycles of anagen (active growth), catagen (transition to no growth), and telogen (dormancy). A typical anagen phase lasts for 2 to 10 years, after which the cells at the base of the hair follicle enter catagen for about 14 to 21 days. At the end of the catagen phase, the follicle enters the telogen phase, and becomes dormant for a period of 30 to 90 days. During this phase, the previously growing hair detaches from the base of the follicle, and is eventually shed from the skin as it is pushed out of the follicle by the growth of new hair strand that occurs when the follicle enters a new anagen phase.
Proper hair growth depends upon maintaining the scalp in its optimal condition, by carefully keeping it nourished, conditioned, and moisturized. However, because the scalp has an abundance of sebaceous glands, it tends to be oilier than skin of many other parts of the body. Therefore, it is helpful to balance the conditioning and moisturization of the scalp with the natural oiliness of the scalp. One way to accomplish this task is through the application of a combination of vitamins, minerals, and herbs instead of (or in addition to) the application of conventional emollients and humectants.
In spite of these general teachings, there is still a need to develop specific hair care formulations and systems that balance the competing needs of the hair and scalp, and enhance the appearance of the hair.